The Ferromagnetic Coupling Between Cu II Ions via the m -Phenylene bridge May be Tuned:
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The Ferromagnetic Coupling Between Cu II Ions via the m-Phenylene bridge May be Tuned: Perspectives from Theory and Experiment Guillem Aromí , Joan Ribas, Juan J. Novoa, Jordi Ribas-Ariño, Debashis Ray Universitat de Barcelona, Departament de Química Inorgànica i CERQT, Diagonal 647, 08028 BARCELONA, Spain Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India The m-phenylene bridge has been suggested as a convenient way to induce ferromagnetic coupling between metallic spin carriers. This is to occur, presumably, through a spin polarization mechanism. Three synthetic [Cu II 2 ] complexes displaying this bridge, including ours, showed very different type of magnetic couplings. This behavior could be well simulated by DFT calculations. The theoretical studies have been extended to a series of model complexes, where the electronic properties of the ligand were modified. A correlation between the strength of the coupling and the total spin population on the central bridge is found, and this can be modulated by choosing appropiately the external substituents of the ligand. Predictions of very strong ferromagnetic interactions with certain ligands offer an attractive challenge to experimetal chemists. INTRODUCTION N N OH OH N H N H O O OH O O OH N N OH OH H 2 L1 H 4 L2 H 2 L3 ) , ( ' ) , ( 2 2 J T F zJ kT T J F TNg T M 1 ) / exp( 3 2 ) , ( kT J T J F 2 1 ˆ ˆ ˆ S S J H Heisenberg Spin Hamiltonian Bleaney-Bowers Equation and Molecular field approximation [Cu 2 (L1) 2 ] (1) [Cu 2 (L2) 2 ] 4+ (2 4+ ) [Cu 2 (L3) 2 ] (3) J exp = -1.0 cm -1 J exp = +16.8 cm -1 J exp = +14.6 cm -1 Hendrickson et al. Inorg. Chem. 1978, 17, 1834 Journaux et al. Angew. Chem. Int. Ed. 2001, 40, 3039 This work For Complex 3 The three ligands and the corresponding [Cu II 2 ] complexes below where prepared and the magnetic coupling determined. The large differences are not obvious to explain. J=+14.56 cm -1 zJ’=-0.98 cm -1 g=2.13 EXPERIMENT J = +4.4 cm 1 N N O O Cu Cu H H H H MODEL B J = +12.3 cm 1 N N O O Cu Cu H F F H MODEL C J = +39.1 cm 1 N N O O Cu Cu H H MODEL E J = +325 cm 1 N N NH 2 H 2 N Cu Cu H H H H H H MODEL F N N O O Cu Cu J = +1.7 cm 1 MODEL A N N O O Cu Cu H 3 C CH 3 H 3 C CH 3 MODEL D J = +14.5 cm 1 A correlation is found between the strength of the ferromagnetic coupling and the total spin population Σ|ρ i | of the phenylene bridge. This is enhanced for ligands favouring localization of charge on the donor atom near the bridge (right form in the scheme below) The couplig within the three experimental systems was simulated correctly by DFT. The coupling within a series of model complexes was also calculated. 0.2 0.4 0.6 0.8 1.0 1.2 0 50 100 150 200 250 300 350 Σ|ρ i | J / cm -1 N N O O R 3 R 1 R 1 R 3 R 2 R 2 N N O O R 3 R 1 R 1 R 3 R 2 R 2 THEORY This work suggests the possibility of tuning the coupling between Cu II ions through a m- phenylene bridge using chemical tools. Ligand in MODEL F is predicted to give a J value of +325 cm -1 . PERSPECTIVES Ministerio de Ciencia y Tecnología (Spain) and the Council of Scientific and Industrial Research (India) are kindly acknowledged ACKNOWLEDGEMENTS This work is featured in the recent publication; Chem. Commun. 2005, 5172-5174
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Transcript of The Ferromagnetic Coupling Between Cu II Ions via the m -Phenylene bridge May be Tuned:
The Ferromagnetic Coupling Between CuII Ions via the m-Phenylene bridge May be
Tuned:Perspectives from Theory and Experiment
Guillem Aromí, Joan Ribas, Juan J. Novoa, Jordi Ribas-Ariño, Debashis RayUniversitat de Barcelona, Departament de Química Inorgànica i CERQT, Diagonal 647, 08028 BARCELONA,
SpainDepartment of Chemistry, Indian Institute of Technology, Kharagpur 721 302, India
The m-phenylene bridge has been suggested as a convenient way to induce ferromagnetic coupling between metallic spin carriers. This is to occur, presumably, through a spin polarization mechanism. Three synthetic [Cu II
2] complexes displaying this bridge, including ours, showed very different type of magnetic couplings. This behavior could be well simulated by DFT calculations. The theoretical studies have been extended to a series of model complexes, where the electronic properties of the ligand were modified. A correlation between the strength of the coupling and the total spin population on the central bridge is found, and this can be modulated by choosing appropiately the external substituents of the ligand. Predictions of very strong ferromagnetic interactions with certain ligands offer an attractive challenge to experimetal chemists.
INTRODUCTION
N N OHOH
NH
NH
O
O
OH
O
O
OH
N N OHOH
H2L1 H4L2 H2L3
),('
),(22
JTFzJkT
TJFTNgTM
1)/exp(32),( kTJTJF
21ˆˆˆ SSJH
Heisenberg Spin Hamiltonian
Bleaney-Bowers Equation and Molecular field approximation
[Cu2(L1)2] (1) [Cu2(L2)2]4+ (24+) [Cu2(L3)2] (3)
Jexp= -1.0 cm-1 Jexp= +16.8 cm-1 Jexp= +14.6 cm-1
Hendrickson et al. Inorg. Chem. 1978, 17, 1834
Journaux et al. Angew. Chem. Int. Ed. 2001, 40, 3039
This work
ForComplex 3
The three ligands and the corresponding [CuII2]
complexes below where prepared and the magnetic coupling determined. The large
differences are not obvious to explain.
J=+14.56 cm-1
zJ’=-0.98 cm-1
g=2.13
EXPERIMENT
J = +4.4 cm1
N N OO
Cu Cu
H H H H
MODEL B
J = +12.3 cm1
N N OO
Cu Cu
H F F H
MODEL C
J = +39.1 cm1
N N OO
Cu Cu
H H
MODEL E
J = +325 cm1
N N NH2H2N
Cu Cu
H H H
H H
H
MODEL F
N N OOCu Cu
J = +1.7 cm1
MODEL A
N N OO
Cu Cu
H3C CH3 H3C CH3
MODEL D J = +14.5 cm1
A correlation is found between the strength of the ferromagnetic coupling and the total spin
population Σ|ρi| of the phenylene bridge. This is enhanced for ligands favouring localization of
charge on the donor atom near the bridge (right form in the scheme below)
The couplig within the three experimental systems was simulated correctly by DFT. The coupling within a series of model complexes was also
calculated.
0.2 0.4 0.6 0.8 1.0 1.2
050
100150200250300350
Σ|ρi|
J / c
m-1
N N OO
R3 R1 R1 R3
R2 R2
N N OO
R3 R1 R1 R3
R2 R2
THEORY
This work suggests the possibility of tuning the
coupling between CuII ions through a m-phenylene
bridge using chemical tools. Ligand in MODEL F is
predicted to give a J value of +325 cm-1.
PERSPECTIVES
Ministerio de Ciencia y Tecnología (Spain) and the Council of Scientific and Industrial Research
(India)are kindly acknowledged
ACKNOWLEDGEMENTS
This work is featured in the recent publication; Chem. Commun. 2005, 5172-5174
